If you're not familiar with what "RAW" means to photographers, you've no doubt at least heard the term. When photographers talk about shooting in RAW, they don't mean they're taking pictures down at the local sushi restaurant. Though sushi does often make for lovely photographs. What photographers mean when they talk about RAW is a file format that all modern DSLRs are capable of shooting in.
Frozen Wave at Sunset by Flickr user Daniel Peckham
What is RAW?
Most cameras default to taking photographs in JPG format, which is a file format you're probably intimately familiar with. JPG is very practical, because it allows you to shoot a lot of images and keep them on a single memory card. Even high resolution JPG files don't take up a ton of space, and they also don't require any processing before you can open them up and look at them.
So why not just stick with JPG? Well, the drawback is that JPG is a compressed image format, which is why you can put so many of them on a single memory card. When you shoot in JPG, your camera makes some decisions about what information it should keep and what it should throw away. As a result, you may get images with blown-out highlights or too-black shadows. Your camera may also decide to sharpen your image, or muck around with the colors. All of this isn't necessarily awful, but it does mean that you've lost a lot of control over what your final image will look like.
Sunset at Botallack by Flickr user HÃ¥kon Iversen Photog - On and off Flickr
When you shoot in RAW, though, your camera captures every single detail it's capable of capturing, and it doesn't do any processing, so you won't lose details just because your camera decided you didn't need them.
Why RAW is a good idea for sunset photography
Now, I'm sure your big question is this: why is this so important for sunsets? Sunsets by their nature have a lot of dynamic range, which means there's a very broad range of brightness between those highlights and shadows. RAW is going to do a much better job capturing all those brightness levels than JPG will. And because when you're shooting a sunset you're always going to be doing a little bit of guesswork (hence the bracketing we've been talking about), RAW is going to help you guess right. The RAW file format naturally captures more information than the JPG format, so you've got more margin for error.
Another benefit of shooting sunsets in RAW is that you can very easily play with your white balance after the fact. This can be great for adding reds to your sky or even for experimenting with other colors that weren't present in the original scene.
One step further - turn your sunsets into HDRs
If you haven't experimented with HDR images, now is the perfect time to start. HDR stands for "high dynamic range", which means that you're taking all those different tones captured by the RAW file format and you're creating an image that has an incredible range of colors and tones and lots of clear detail. Many HDR images are actually combined shots taken at different exposures—they have so much tonal range that they often look surreal.
I'm not going to go into a lot of detail about processing HDR files (see my HDR articles for that) but here are a few tips on how to capture them.
Remember because you're shooting in RAW that you're already capturing more dynamic range than you would be in JPG. So bracket, but you can put as much as two stops difference between each image because you're already capturing so much extra information in those RAW files that you just don't need all those additional shots. Remember that you should only change shutter speed, not f-stop, because you don't want the depth of field to change between shots. Make sure you end up with a couple of images that look pretty good on your histogram, and a couple that look really underexposed and really overexposed. That's how you get that great range of tones.
Oia, Santorini by Flickr user szeke
A tripod and cable release (or your camera's timer) are essential when shooting HDR, because you're going to be combining images in post-processing and you need them to line up properly. You don't want any camera shake, and you also want the images to be identical with the exception of the exposure itself. You'll also need that tripod because ideally you want to be shooting at low ISOs, which means slower shutter speeds especially when the sun disappears behind the horizon.
While you're at it, shoot some panoramas. Remember that you need to use manual mode for these, because you don't want your exposure to change as you move from one part of the scene to another. And don't change other settings, either. Your focal length and focus should be the same from one image to the next.
Sunset at the tide pools. La Jolla by Flickr user moreno1024
A couple of other tips you might find useful: make sure you've got plenty of overlap between one photo and another, because that will make it much easier to stitch the files together in post processing. And try shooting vertically (with your camera on it's side) instead of horizontally. That way you'll capture a lot more of the sky and landscape, and you'll have more room to crop the images later on if it's necessary. When shooting vertically you will have to capture more images than you would if you were shooting horizontally, so make sure you work fast to cope with the fading light.
You can go a lot of places with your sunset photography and achieve some really wowing results. It may take some time for you to get there (sadly, we only get one chance a day to shoot those sunsets, and one chance to shoot the sunrise) but it still pays to practice and experiment. Shooting in RAW is a great place to start, because it gives you a better chance at getting that perfect exposure you're looking for. Once you've mastered those RAW sunset shots, try HDR and panoramas—you'll be thrilled with what they do for your portfolio.